1. Field of the Invention
The invention belongs to the field of feeds, and particularly relates to a feed additive of p-thymol, a salt or an ester derivative thereof for use in a complete formula feed.
2. Description of the Prior Art
The usage of feed antibiotics (AGPs) was regarded as the greatest biotechnology in animal husbandry production in the 20th century. It was first reported that streptomycin can stimulate the growth of chicken in 1946, and Food and Drug Administration (FDA) first approved that antibiotics were used as feed additives in 1950. Hereafter, the antibiotics are widely used for treating and preventing bacterial diseases, and are also popularized and applied in a large range as the feed additives, so the antibiotics play an extremely important role in controlling infectious diseases of livestock and poultry and promoting the healthy development of modern breeding industry. However, with more and more use and more and more abuse of the antibiotics, various shortcomings of the antibiotics are gradually recognized by people. The negative effects of the antibiotics serving as the feed additives mainly comprise the following several aspects: firstly, drug-resistant strains are generated, and the occurrence of a large quantity of drug-resistant strains, particularly multiple-resistant strains arouses the worry of people about bacterial drug resistance transfer, so that concern on the problem of public health is aroused; secondly, the growth promoting effect of the antibiotics significantly declines due to the drug-resistant strains, and the antibiotics overdose often occurs clinically, so that the drug resistance of bacteria is more serious, and on the contrary, the toxic and side effects of the antibiotics overdose inhibit the production performance of animals and affect the normal physiological functions of the animals; and finally, long-term use and abuse of the feed antibiotics lead to residue in animal products and the environment and harm the health of human beings. Based on the consideration of multiple aspects, the European Union has comprehensively banned the use of the feed antibiotics as animal growth promoters since 2006, and Korea has also prohibited 8 feed growth promoting antibiotics including enramycin in feeds since August, 2010. Particularly, after the “super bacteria” event in 2010, the doubt about the use of the feed antibiotics and the voice for prohibition has been growing. Therefore, the research and development of effective antibiotic substitutes become an important direction in the development of the feed additive industry.
A lot of work has been done on the research of feed antibiotic substitutes. In the substitutes such as edible essential oil, organic acid, enzyme preparation, oligosaccharides and micro-ecological preparations, the use of essential oil components to substitute the antibiotic growth promoters is the most requested.
Majoram, also named as dysentery stop herb, elsholtzia patrini garcke and lobular mint, is a lamiaceae origanum renascent herb. An essential oil extract, namely majoram oil, which is extracted from the natural majoram plant, is light yellow clear oily liquid. At present, the majoram oil has been approved to be used as a feed additive for improving the production performance of livestock and poultry, and is greatly used in European Union countries as a substitute for antibiotic growth promoters.
The majoram oil contains more than 30 components, wherein the main components are carvacrol and thymol which account for 60-70% and 10-20% of the total amount of the majoram oil respectively. Further research has proved that the antibacterial activity of the majoram oil and the effect as the animal growth promoter are mainly from the effects of thymol and carvacrol. Thymol is also named as ‘Shexiangcaofen’, of which the chemical name is 5-methyl-2-isopropyl-phenol, the melting point is 51.5° C., the boiling point is 232° C., and the oral median lethal dose (LD50) of rats is 980 mg/kg weight. Carvacrol is an isomeride of thymol, of which the chemical name is 2-methyl-5-isopropyl-phenol, the melting point is about 0° C., the boiling point is 237-238° C., and the oral median lethal dose (LD50) of the rats is 810 mg/kg weight.
Although the production performance of animals can be partially improved when the majoram oil taking thymol and carvacrol as main components is used as a feed additive, the defects of the majoram oil limit the application in the feed industry on three aspects: (1) the strong pungent smell affects feed processing and also reduces the intake of the animals; (2) the majoram oil has strong volatility, so that the majoram oil is easy to volatilize in the feed preservation process and must be used in a large dose; and (3) thymol and carvacrol have relatively strong toxicity on the animals (the oral LD50 of the rats are 980 mg/kg weight and 810 mg/kg weight respectively), narrow safety range and weak mutability.